The invention relates to a drag and/or dip finishing machine for the surface machining of workpieces, by means of grinding and/or polishing granules, by movement of the workpieces in a bed of the grinding and/or polishing granules relative to said bed with the addition of a liquid machining agent, comprising at least one workpiece holder for the releasable fastening of the workpieces to be machined and comprising a container, disposed beneath the workpiece holder, for accommodating the grinding and/or polishing granules, wherein the workpiece holder and the container are movable relative to each other in that at least the container is rotationally driven.
The working method of drag and/or dip finishing machines of this type is based on dipping the workpiece to be machined into a bed of the grinding and/or polishing granules located in a container and on moving the workpiece relative to the granules, whereby the surface of the workpiece is ground and/or polished according to the nature of the granules. Drag finishing machines represent a specific form of vibratory grinding machines, wherein the workpieces to be machined can be clamped, for example, individually on one or more clamping devices of a workpiece holder. They frequently comprise a generally rotary part, substantially in the form of a plate which is rotationally driven, for example, by motorized means via a suitable gear mechanism and on which the workpiece holders are fixed directly or indirectly, for instance via lifting devices. This is realized, in particular, eccentrically in relation to the rotational axis of the rotary part of the drag finishing machine. If this part—the so-called plate—of the drag finishing machine is rotated, then the workpiece holders fixed hereon describe a path curve. The workpieces supported by the workpiece holders are hereupon dipped into the working container, which is filled with the bed of the particulate grinding or polishing granules, frequently with the addition of liquid machining agents, such as water, surfactants, etc. Due to the relative motion of the workpieces in relation to the granules, their surface machining is effected in the form of a vibratory grinding machining. Drag finishing machines of this type are known, for instance, from DE 102 04 267 C1, DE 200 05 361 U1 or DE 10 2010 052 222 A1.
Alternatively or additionally, the container which accommodates the machining agent can be moved relative to the workpieces—which are likewise moved, for instance are rotated at least about their own axis, or else are static—such as, for instance, about its own axis and/or along a path curve, for example in the form of a circular path. Insofar as only the container is moved and the workpieces themselves perform no translatory motion, then this is also referred to as “plunge-cut grinding” or “immersion polishing”.
The grinding or polishing granules can in principle, according to the workpieces to be treated, be very different in nature and, for example, of natural origin (for example of organic material, such as walnut or coconut shells, wood, cherry pit, etc.), of mineral origin (for example of silicates, oxides, etc.) and/or of synthetic origin (for example of plastics). Furthermore—as already indicated—it is possible to perform the vibratory grinding machining dry or—with the addition of a liquid machining agent, such as, for instance, water, to which additives, such as, for example, surfactants, can be added—in the form of a wet machining.
In order to ensure, in addition to a translatory motion of the workpieces relative to the particulate machining agent, also a rotatory motion of the workpieces, such as about their own axis, which yields a particularly effective grinding or polishing effect, the workpiece holders of known drag finishing machines are frequently rotationally driven, which can be realized, for instance, by means of suitable motors (DE 10 2010 052 222 A1). In addition, workpiece holders for drag finishing machines, the clamping devices of which, for the releasable fastening of the workpieces, are rotatably mounted and can be set in rotation via a shaft mounted rotatably in the workpiece holder, are known. To this end, the workpiece holder has, for example, a planetary gearing having a central sun gear, which is engaged with planetary gears which, for their part, are connected in a rotationally secure manner to a bearing shaft of a respective tension lock and which are arranged distributed around the periphery of the sun gear of the workpiece holder. Due to such a movement of the clamping devices, rotatably mounted on the workpiece holder, with the workpieces, which movement is composed of a translatory motion (in the rotational direction of the carrying part or of the “plate” of the drag finishing machine) and a rotatory motion (about the axis of the respective clamping device or about the workpiece axis), a very even machining quality, combined with considerably shorter machining times compared with a purely translatory motion, is obtained by virtue of the machining agent. Alternatively or additionally, furthermore, the workpiece holder itself can be fixed in a corresponding manner on the carrying part of the drag finishing machine (DE 20 2009 008 070 U1).
A problem with the vibratory grinding or polishing machining can consist in the fact that, particularly in the case of the frequently applied wet machining in the presence of a liquid machining agent, during the abrasive contact of the workpieces with the grinding or polishing granules an increasing contamination of the machining agent takes place, which not only calls for a more or less frequent exchange of the machining agent, but can also result in a sticky deposit on the workpieces, so that these must subsequently be cleaned or there is even the risk of deficient surface machining. The contamination can stem, on the one hand, directly from the grinding stock to be machined, but also from the grinding or polishing granules themselves, which, with increasing residence time, are subjected to a progressive, fine-particle abrasion. If plastics granules (whether with or without grinding agents embedded herein) are used, which plastics granules, due to their easily precisely adjustable characteristics, such as hardness, particle size fraction, grain shape, etc., are particularly suitable per se, then there is the added factor that, during the abrasive contact of such granules with the workpieces to be machined, plastics components, for example resin components, plastics additives, such as plasticizers or the like, which can lead to still faster formation of a layer-forming and sticky deposit on the workpieces, which deposit, moreover, can be satisfactorily removed only with difficulty, can separate off from the granules.
In order to counter this, various additives, such as, for instance, commercially available surfactants, are widely added to the machining agent, yet it has been shown that surfactants are only very limitedly capable of reducing said deposits. A, by comparison, significantly more effective additive based on poly (2-hydroxyalkyl-1-N-alkylammonium halogenides) or poly (2-hydroxyalkyl-1,1-N-dialkylammonium halogenides) is known from DE 10 2009 004 916 A1, yet it is nevertheless desirable, particularly in the case of relatively long machining times, to exchange the machining agent even when such additives have been added thereto.
Furthermore, there is quite often the need for a grinding or polishing machining using different quantities of the added liquid machining agent in order to be able to modify the abrasive effect made on the respective workpiece by the granule particles.
While it is the case that the liquid machining agent can be added without difficulty to the rotationally driven drag or dip finishing machine of the generic type, whether manually or automatically by means of control valves, an evacuation of the liquid machining agent from the container proves complicated and normally requires an interruption of the running of the machine. DE 20 2010 010 546 U1 describes a drag finishing machine having a drain, provided in the central lower region of the stationary container, for a liquid machining agent, so that the latter can be discharged even while the machine is running. However, such a construction proves complicated in design if the container is to be rotated by means of a suitable drive, while, on the other hand, a control or regulation of the respectively desired quantity of liquid machining agent in the container is barely possible.
The object of the invention is therefore to refine a drag and/or dip finishing machine for the surface machining of workpieces, of the type stated in the introduction, in a simple and cost-effective manner and with at least extensive avoidance of the aforesaid drawbacks such that, in wet machining of the workpieces with the addition of a liquid machining agent, an exchange of this same is possible without having to interrupt the running of the machine, wherein, in particular, a simple control of the desired quantity of machining agent should also be possible.